JP6861253B2 - Liquid crystal display device - Google Patents

Description

The present invention relates to a semiconductor device and a method for manufacturing the semiconductor device.

In the present specification, the semiconductor device refers to all devices that can function by utilizing the semiconductor characteristics, and the electro-optical device, the semiconductor circuit, and the electronic device are all semiconductor devices.

Attention is being paid to a technique for forming a transistor (also referred to as a thin film transistor (TFT)) using a semiconductor thin film formed on a substrate having an insulating surface. The transistor is an integrated circuit (
It is widely applied to electronic devices such as ICs) and image display devices (display devices). Silicon-based semiconductor materials are widely known as semiconductor thin films applicable to transistors, but oxide semiconductors are attracting attention as other materials.

For example, a transistor using an amorphous oxide containing indium (In), gallium (Ga), and zinc (Zn) having ^{an electron carrier concentration of less than 10 18} / cm ^{3 is disclosed as the active layer of the transistor.} (See Patent Document 1).

Japanese Unexamined Patent Publication No. 2006-165528

However, in the thin film forming process, the electrical conductivity of oxide semiconductors changes when they deviate from the stoichiometric composition due to excess or deficiency of oxygen or when hydrogen or water that forms electron donors is mixed. It ends up. Such a phenomenon becomes a factor of fluctuation in electrical characteristics for a transistor using an oxide semiconductor.

In view of such a problem, one of the purposes is to impart stable electrical characteristics to a semiconductor device using an oxide semiconductor and to improve reliability.

Another object of the present invention is to prevent the generation of parasitic channels on the back channel side of the oxide semiconductor film.

In order to suppress fluctuations in the electrical characteristics of transistors that use oxide semiconductor films, impurities such as hydrogen, water, hydroxyl groups, and hydrides (also called hydrides) that cause fluctuations are intentionally removed from the oxide semiconductor membrane. Moreover, by supplying oxygen, which is a main component material constituting the oxide semiconductor, which is reduced at the same time by the removal process of impurities, the oxide semiconductor film is highly purified and electrically made i-type (intrinsic).

An i-type (intrinsic) oxide semiconductor is an i-type by removing hydrogen, which is an n-type impurity, from the oxide semiconductor and purifying it so that impurities other than the main component of the oxide semiconductor are not contained as much as possible. (
It is an oxide semiconductor of (intrinsic) or an oxide semiconductor of type i (intrinsic) as close as possible. That is, it is characterized in that impurities such as hydrogen and water are removed as much as possible instead of adding impurities to form i-type, so that the i-type (intrinsic semiconductor) with high purity or close to it can be obtained. By doing so, the Fermi level (Ef) can be brought to the same level as the true Fermi level (Ei).

In a transistor containing an oxide semiconductor film, an oxide layer having an antistatic function is formed in contact with the oxide semiconductor film and heat-treated.

The oxide layer having an antistatic function is preferably provided on the back channel side (opposite side of the gate insulating film) of the oxide semiconductor film, preferably the highly purified oxide semiconductor film. Further, the oxide layer having an antistatic function preferably has a smaller dielectric constant than that of an oxide semiconductor. For example, it is preferable to use an oxide layer having a dielectric constant of 8 or more and 20 or less.

The oxide layer is thicker than the thickness of the oxide semiconductor film. For example, the thickness of the oxide semiconductor film is preferably 3 nm or more and 30 nm or less, and the oxide layer is preferably a film thickness of more than 10 nm and a film thickness of the oxide semiconductor film or more.

A metal oxide can be used as the oxide layer. As the metal oxide, for example, gallium oxide or gallium oxide to which indium or zinc is added in an amount of 0.01 to 5 atomic% can be used.

The oxide semiconductor film can be made highly purified by intentionally removing impurities such as hydrogen, water, hydroxyl groups or hydrides (also referred to as hydrides) from the oxide semiconductor film by a heating step. preferable. By heat treatment, hydrogen or hydroxyl group, which is an impurity, is converted into water.
It can be easily detached.

In addition, since the heat treatment is performed in a state where the metal oxide film containing oxygen and the oxide semiconductor film are in contact with each other, oxygen, which is one of the main component materials constituting the oxide semiconductor, is reduced at the same time by the removal process of impurities. Can be supplied from a metal oxide film containing oxygen to an oxide semiconductor film. Therefore, the oxide semiconductor film is made more pure and electrically made i-type (intrinsic).

Further, after the heat treatment, a protective insulating layer that blocks impurities such as water and hydrogen from entering from the outside may be further formed on the metal oxide film so as not to be remixed into the oxide semiconductor film. ..

Transistors having a highly purified oxide semiconductor film have almost no temperature dependence on electrical characteristics such as threshold voltage and on-current. In addition, there is little fluctuation in transistor characteristics due to photodegradation.

As described above, the transistor having a highly purified and electrically i-type (intrinsic) oxide semiconductor film has suppressed electrical characteristic fluctuations and is electrically stable. Therefore, it is possible to provide a highly reliable semiconductor device using an oxide semiconductor having stable electrical characteristics.

The temperature of the heat treatment is 250 ° C. or higher and 650 ° C. or lower, or 450 ° C. or higher and 600 ° C. or lower, or lower than the distortion point of the substrate. The heat treatment is nitrogen, oxygen, ultra-dry air (water content is 20p).
It may be carried out in an atmosphere of pm or less, preferably 1 ppm or less, preferably 10 ppb or less) or a rare gas (argon, helium, etc.).

One form of the configuration of the invention disclosed in the present specification includes a gate electrode, a gate insulating film covering the gate electrode, an oxide semiconductor film in a region overlapping the gate electrode on the gate insulating film, and an oxide semiconductor film. It is a semiconductor device having a source electrode and a drain electrode in contact with each other, and a metal oxide film in contact with an oxide semiconductor film and covering the source electrode and the drain electrode.

In the above configuration, it is preferable to use a gallium oxide film as the metal oxide film. The gallium oxide film can be obtained by a sputtering method, a CVD method, a vapor deposition method or the like. The gallium oxide film has a bandgap of about 4.9 eV and is translucent in the visible light region, although it depends on the composition ratio of oxygen and gallium.

In this specification, gallium oxide may be referred to as GaOx (x> 0). For example, Ga
When Ox has a crystal structure, Ga ₂ O ₃ with x = 1.5 is known.

In the above configuration, the metal oxide film is preferably composed of a gallium oxide film containing 0.01 to 5 atomic% of indium or zinc. Further, the difference between the band gap of the metal oxide film and the band gap of the oxide semiconductor film is preferably less than 3.0 eV.

Further, the oxide semiconductor film is preferably composed of indium and gallium.

Further, in the above configuration, the source electrode and the drain electrode are preferably configured to include a conductive material having a work function of 3.9 eV or more. The conductive material having a work function of 3.9 eV or more is preferably tungsten nitride or titanium nitride.

Further, in one embodiment of the present invention, a gate electrode is formed on a substrate, a gate insulating film covering the gate electrode is formed, and an oxide semiconductor film is formed in a region overlapping the gate electrode via the gate insulating film. This is a method for manufacturing a semiconductor device in which a source electrode and a drain electrode are formed on an oxide semiconductor film, a metal oxide film covering the oxide semiconductor film, the source electrode and the drain electrode is formed, and heat treatment is performed.

In the above configuration, it is preferable to form a film containing gallium oxide as the metal oxide film. Further, as the metal oxide film, it is preferable to form a gallium oxide film containing 0.01 to 5 atomic% of indium or zinc. The temperature of the heat treatment is preferably 450 ° C to 600 ° C.

In one embodiment of the present invention, a metal oxide film is formed in contact with the oxide semiconductor film and heat-treated.
By this heat treatment, impurities such as hydrogen, water, hydroxyl groups, and hydrides can be intentionally removed from the oxide semiconductor film, and the oxide semiconductor film can be made highly purified. A transistor having a highly purified and electrically i-type (intrinsic) oxide semiconductor film has suppressed electrical characteristic fluctuations and is electrically stable.

Therefore, one embodiment of the present invention can produce a transistor having stable electrical characteristics.

Moreover, one embodiment of the present invention can manufacture a semiconductor device having a transistor having good electrical characteristics and high reliability.

The figure explaining one form of the semiconductor device and the manufacturing method of the semiconductor device. The figure explaining one form of the semiconductor device. The figure explaining one form of the semiconductor device. The figure explaining one form of the semiconductor device. The figure explaining one form of the semiconductor device. The figure explaining one form of the semiconductor device. The figure which shows the electronic device. The figure which shows the electronic device. (A) A model diagram showing a laminated structure of dielectrics, (B) an equivalent circuit diagram.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and it is easily understood by those skilled in the art that the form and details thereof can be changed in various ways. Further, the present invention is not construed as being limited to the description contents of the embodiments shown below.

The ordinal numbers attached as the first and second numbers are used for convenience and do not indicate the process order or the stacking order. In addition, this specification does not indicate a unique name as a matter for specifying the invention.

(Embodiment 1)
In the present embodiment, one embodiment of the semiconductor device and the method for manufacturing the semiconductor device will be described with reference to FIG. In this embodiment, a transistor having an oxide semiconductor film is shown as an example of a semiconductor device.

As shown in FIG. 1D, the transistor 410 includes a gate electrode 401, a gate insulating film 402, an oxide semiconductor film 403, a source electrode 405a, and a drain electrode 405b on a substrate 400 having an insulating surface. On the oxide semiconductor film 403, a metal oxide film 407 having an antistatic function on the back channel side of the oxide semiconductor film 403 is provided.

1 (A) to 1 (D) show an example of a method for manufacturing the transistor 410.

First, a conductive film is formed on the substrate 400 having an insulating surface, and then the gate electrode 401 is formed by the first photolithography step. The resist mask may be formed by an inkjet method. When the resist mask is formed by the inkjet method, the photomask is not used, so that the manufacturing cost can be reduced.

There is no major limitation on the substrate that can be used for the substrate 400 having an insulating surface, but it is necessary that the substrate has at least heat resistance enough to withstand the subsequent heat treatment. For example, a substrate such as a glass substrate, a ceramic substrate, a quartz substrate, or a sapphire substrate can be used. Further, as long as it has an insulating surface, it is possible to apply a single crystal semiconductor substrate such as silicon or silicon carbide, a polycrystalline semiconductor substrate, a compound semiconductor substrate such as silicon germanium, an SOI substrate, or the like. Transistors 410 may be made on top.

Further, a flexible substrate may be used as the substrate 400. When a flexible substrate is used, the transistor 410 containing the oxide semiconductor film 403 may be directly manufactured on the flexible substrate, or the transistor 410 containing the oxide semiconductor film 403 may be manufactured on another production substrate. After that, it may be peeled off and transferred to a flexible substrate. In addition, in order to peel and transfer from the manufactured substrate to the flexible substrate, it is preferable to provide a peeling layer between the manufactured substrate and the transistor containing the oxide semiconductor film.

An insulating film serving as a base film may be provided between the substrate 400 and the gate electrode 401. The undercoat film has a function of preventing the diffusion of impurity elements from the substrate 400, and is formed of one or more films selected from a silicon nitride film, a silicon oxide film, a silicon oxide film, or a silicon nitride film. Can be done.

Further, the gate electrode 401 may be formed in a single layer or laminated using a metal material such as molybdenum, titanium, tantalum, tungsten, aluminum, copper, neodymium, scandium or an alloy material containing these as main components. it can.

Next, the gate insulating film 402 is formed on the gate electrode 401. The gate insulating film 402 is
Silicon oxide film, silicon nitride film, etc. using plasma CVD method or sputtering method, etc.
Silicon oxide film, silicon nitride film, aluminum oxide film, aluminum nitride film,
It can be formed by one or more films selected from an aluminum nitride film, an aluminum nitride film, or a hafnium oxide film.

Further, the oxide semiconductor film 403 of the present embodiment is intrinsic (i) by removing impurities and purifying the oxide semiconductor film 403 so as not to contain impurities that serve as carrier donors other than the main component of the oxide semiconductor as much as possible. Oxide semiconductors that have been typed or substantially intrinsic (i type) are used. Specifically, for example, the hydrogen concentration of the oxide semiconductor film 403 is 5 × 10 ¹⁹ atoms / cm ³ or less, preferably 5 × 10 ¹⁸ atoms / cm ³ or less, and more preferably 5 × 10 ¹⁷ atoms / c.
It shall be m ^{3 or less.} The hydrogen concentration in the oxide semiconductor film 403 described above is determined by secondary ion mass spectrometry (SIMS: Secondary Ion Mass Spectroscopy).
It is measured at. As described above, in the oxide semiconductor film 403 in which the hydrogen concentration is sufficiently reduced to be highly purified and the defect level in the energy gap due to oxygen deficiency is reduced by supplying sufficient oxygen, the carrier concentration is 1. × 10 ¹² / cm ^{less than 3} , preferably 1 ×
It ^{is less than 10 11} / cm ³ , more preferably less than 1.45 × 10 ¹⁰ / cm ³ . For example, the off-current at room temperature (25 ° C.) (here, the value per unit channel width (1 μm)) is 1.
It is 00 zA (1 zA (zeptoampere) is 1 × ^10-21 A) or less, preferably 10 zA or less. As described above, by using an i-type (intrinsicized) or substantially i-type oxide semiconductor, a transistor 410 having extremely excellent off-current characteristics can be obtained.

Since such a highly purified oxide semiconductor is extremely sensitive to the interface state or the interface charge, the interface between the oxide semiconductor film and the gate insulating film is important. Therefore, high quality is required for the gate insulating film in contact with the highly purified oxide semiconductor.

For example, high-density plasma CVD using μ waves (for example, frequency 2.45 GHz) is preferable as a method for producing a gate insulating film because it can form a dense and high-quality insulating layer having a high dielectric strength. This is because the high-purity oxide semiconductor and the high-quality gate insulating film are in close contact with each other, so that the interface state density can be reduced and the interface characteristics can be improved.

Of course, other film forming methods such as a sputtering method and a plasma CVD method can be applied as long as a high-quality insulating film can be formed as the gate insulating film. Further, the insulating film may be an insulating film in which the film quality of the gate insulating film and the interface characteristics with the oxide semiconductor are modified by heat treatment after the oxide semiconductor film is formed. In any case, not only the film quality as the gate insulating film is good, but also the interface level density with the oxide semiconductor can be reduced and a good interface can be formed.

Further, in order to prevent hydrogen, hydroxyl groups and moisture from being contained in the gate insulating film 402 and the oxide semiconductor film as much as possible, as a pretreatment for film formation of the oxide semiconductor film, the gate electrode 401 is placed in the preheating chamber of the sputtering apparatus. It is preferable that the substrate 400 on which the above is formed or the substrate 400 on which the gate insulating film 402 is formed is preheated to remove impurities such as hydrogen and moisture adsorbed on the substrate 400 and exhausted. A cryopump is preferable as the exhaust means provided in the preheating chamber. The preheating process may be omitted. Further, this preheating may be similarly performed on the substrate 400 (before the formation of the metal oxide film 407) formed up to the source electrode 405a and the drain electrode 405b in a later step.

Next, an oxide semiconductor film having a film thickness of 3 nm or more and 30 nm or less is formed on the gate insulating film 402 by a sputtering method. If the film thickness of the oxide semiconductor film is made too large (for example, the film thickness is 5).
(0 nm or more), the transistor may be normally turned on, so the above-mentioned film thickness is preferable.

Before the oxide semiconductor film is formed by the sputtering method, argon gas is introduced to perform reverse sputtering to generate plasma, and powdery substances (particles and dust) adhering to the surface of the gate insulating film 402 are performed. It is preferable to remove the). The reverse sputtering is a method of modifying the surface by forming plasma in the vicinity of the substrate by applying a voltage to the substrate side using an RF power supply in an argon atmosphere without applying a voltage to the target side. In addition, nitrogen, helium, oxygen and the like may be used instead of the argon atmosphere.

The oxide semiconductor used for the oxide semiconductor film is In-Sn-G, which is a quaternary metal oxide.
a-Zn-O-based oxide semiconductors, In-Ga-Zn-O-based oxide semiconductors that are ternary metal oxides, In-Sn-Zn-O-based oxide semiconductors, In-Al-Zn-O Oxide semiconductors,
Sn-Ga-Zn-O-based oxide semiconductor, Al-Ga-Zn-O-based oxide semiconductor, Sn-A
l-Zn-O-based oxide semiconductors, In-Zn-O-based oxide semiconductors that are binary metal oxides, Sn-Zn-O-based oxide semiconductors, Al-Zn-O-based oxide semiconductors, Zn -Mg-O-based oxide semiconductor, Sn-Mg-O-based oxide semiconductor, In-Mg-O-based oxide semiconductor, In-G
a-O-based oxide semiconductors, In-O-based oxide semiconductors, Sn-O-based oxide semiconductors, Zn-O
A system oxide semiconductor or the like can be used. Further, the oxide semiconductor may contain _{SiO 2.} Here, for example, the In-Ga-Zn-O-based oxide semiconductor is indium (In).
), Gallium (Ga), and zinc (Zn), and the composition ratio is not particularly limited. Further, elements other than In, Ga and Zn may be contained.

Further, as the oxide semiconductor film, _{a thin film represented by the chemical formula InMO 3} (ZnO) _m (m> 0) can be used. Here, M represents one or more metal elements selected from Ga, Al, Mn and Co. For example, as M, Ga, Ga and Al, Ga and Mn, or G.
There are a and Co and the like.

When an In-Ga-Zn-O-based material is used as the oxide semiconductor, the target to be used is, for example, In ₂ O ₃ : Ga ₂ O ₃ : ZnO = 1: 1: 1 [mol number ratio] as the composition ratio. ] Oxide target can be used. Further, the material and composition of the target are not limited, and for example, _{an oxide target of In 2} O ₃ : Ga ₂ O ₃ : ZnO = 1: 1: 2 [mol number ratio] may be used.

When an In—Zn—O-based material is used as the oxide semiconductor, the composition ratio of the target to be used is In: Zn = 50: 1 to 1: 2 in terms of atomic number ratio (In _{2 when converted to a molar ratio).} O ₃
: ZnO = 25: 1 to 1: 4), preferably In: Zn = 20: 1 to 1: 1 (In ₂ O ₃ : ZnO = 10: 1 to 1: 2 when converted to a molar ratio), more preferably. Is In: Zn = 1
It is set to 5: 1 to 1.5: 1 (in ₂ O ₃ : ZnO = 15: 2 to 3: 4 when converted to a molar ratio). For example, the target used for forming the In—Zn—O-based oxide semiconductor is Z> 1.5X + Y when the atomic number ratio is In: Zn: O = X: Y: Z.

The filling rate of the target is 90% or more and 100% or less, preferably 95% or more and 99.9%.
It is as follows. By using a target having a high filling rate, the formed oxide semiconductor film can be made into a dense film.

In the present embodiment, an In-Ga-Zn-O-based oxide target is used as the oxide semiconductor film and a film is formed by a sputtering method. Further, the oxide semiconductor film can be formed by a sputtering method in a rare gas (typically argon) atmosphere, an oxygen atmosphere, or a mixed atmosphere of a rare gas and oxygen.

As the sputter gas used for forming the oxide semiconductor film, it is preferable to use a high-purity gas from which impurities such as hydrogen, water, hydroxyl groups and hydrides have been removed.

The oxide semiconductor film is formed by holding the substrate 400 in a film forming chamber kept under reduced pressure and setting the substrate temperature at 100 ° C. or higher and 600 ° C. or lower, preferably 200 ° C. or higher and 400 ° C. or lower. Board 4
By forming a film while heating 00, the concentration of impurities contained in the formed oxide semiconductor film can be reduced. In addition, damage due to sputtering is reduced. Then, a sputter gas from which hydrogen and water have been removed is introduced while removing residual water in the film forming chamber, and an oxide semiconductor film is formed on the substrate 400 using the target. In order to remove the residual moisture in the film forming chamber, it is preferable to use an adsorption type vacuum pump, for example, a cryopump, an ion pump, or a titanium sublimation pump. Further, the exhaust means may be a turbo pump to which a cold trap is added. In the deposition chamber which is evacuated with a cryopump, for example, hydrogen atom, for such as water (H 2 _O) compound containing a hydrogen atom (preferably, a compound including a carbon atom), and the like, the deposition The concentration of impurities contained in the oxide semiconductor film formed in the chamber can be reduced.

As an example of film formation conditions, the distance between the substrate and the target is 100 mm, and the pressure is 0.6 Pa.
, Direct current (DC) power supply 0.5 kW, conditions under oxygen (oxygen flow rate ratio 100%) atmosphere are applied. It is preferable to use a pulsed DC power supply because powdery substances (also referred to as particles and dust) generated during film formation can be reduced and the film thickness distribution becomes uniform.

Next, the oxide semiconductor film is subjected to a second photolithography step to form an island-shaped oxide semiconductor film 4
It is processed into 41 (see FIG. 1 (A)). Further, a resist mask for forming the island-shaped oxide semiconductor film 441 may be formed by an inkjet method. When the resist mask is formed by the inkjet method, the photomask is not used, so that the manufacturing cost can be reduced. As a result, an oxide semiconductor film in a region overlapping the gate electrode can be formed on the gate insulating film.

The etching of the oxide semiconductor film here may be dry etching or wet etching, or both may be used. For example, as the etching solution used for wet etching of the oxide semiconductor film, a solution obtained by mixing phosphoric acid, acetic acid, and nitric acid can be used. Further, ITO07N (manufactured by Kanto Chemical Co., Inc.) may be used.

Next, a conductive film for forming a source electrode and a drain electrode (including wiring formed in the same layer) is formed on the gate insulating film 402 and the oxide semiconductor film 441. Examples of the conductive film used for the source electrode and the drain electrode include Al, Cr, Cu, Ta, and Ti.
, Mo, a metal film containing an element selected from W, a metal nitride film containing the above-mentioned elements as a component (titanium nitride film, molybdenum nitride film, tungsten nitride film) and the like can be used.
Further, a refractory metal film such as Ti, Mo, W or a metal nitride film thereof (titanium nitride film, molybdenum nitride film, tungsten nitride film) is formed on one or both of the lower side or the upper side of the metal film such as Al and Cu. May be a laminated structure. Further, the conductive film used for the source electrode and the drain electrode may be formed of a conductive metal oxide. Conductive metal oxides of indium oxide _{(In 2 O} 3), tin oxide _(SnO 2), zinc oxide (ZnO), _(abbreviated as _{In 2 O 3 -SnO 2, ITO} ) of indium oxide and tin oxide alloy, Indium zinc oxide zinc oxide alloy (In ₂ O _3- ZnO) or a metal oxide material containing silicon oxide can be used.

The materials of the source electrode and the drain electrode are preferably determined in consideration of the electron affinity of the oxide semiconductor used and the electron affinity of the metal oxide film. That is, when the work function of the material of the source electrode and the drain electrode is W [eV], the electron affinity of the oxide semiconductor is φ ₁ [eV], and the electron affinity of the metal oxide film is φ ₂ [eV], φ ₂ +0. _{.4 <W <(φ 1 +0.5} ),
_{Preferably, (φ 2 +0.9) <W} <(φ 1 +0.4), it is preferable to satisfy the relationship. For example, as an oxide semiconductor and a metal oxide film, the electron affinity is 4.5 eV, respectively.
If 3.5 eV materials are used, the source and drain electrode materials have work functions greater than 3.9 eV and less than 5.0 eV, preferably greater than 4.4 eV and less than 4.9 eV. It is preferable to use a certain metal or metal compound. Thus, in the transistor 410, the injection of electrons from the source electrode 405a and the drain electrode 405b into the metal oxide film 407 can be prevented, the leakage current can be suppressed, and the oxide semiconductor film is bonded to the source electrode and the drain electrode. Good electrical characteristics can be obtained in. Examples of the material having such a work function include molybdenum nitride and tungsten nitride. These materials are preferable because they are also excellent in heat resistance. Note that the above _{relation, φ 2 <(φ 1 +0.1} ), but preferably relational expression φ ₂ <(φ ₁ -0.5) is derived, and more preferably, φ ₂ <(φ ₁ It is good to satisfy the relationship of −0.9).

A resist mask is formed on the conductive film used for the source electrode and the drain electrode by the third photolithography step, and is selectively etched to form the source electrode 405a and the drain electrode 405b, and then the resist mask is removed (. See FIG. 1 (B)).

Ultraviolet rays, KrF laser light, or ArF laser light may be used for the exposure at the time of forming the resist mask in the third photolithography step. The channel length L of the transistor to be formed later is determined by the distance between the lower end of the source electrode 405a adjacent to each other on the oxide semiconductor film 441 and the lower end of the drain electrode 405b. When exposure is performed with a channel length of less than L = 25 nm, ultra-ultraviolet rays (Extreme Ultra) having an extremely short wavelength of several nm to several tens of nm are used.
It is preferable to perform the exposure at the time of forming the resist mask in the third photolithography step using a labiolet). Exposure with ultra-ultraviolet rays has a high resolution and a large depth of focus. Therefore, the channel length L of the transistor formed later can be set to 10 nm or more and 1000 nm or less, and the operating speed of the circuit can be increased.

Further, in order to reduce the number of photomasks and the number of steps used in the photolithography step, even if the etching step is performed using a resist mask formed by a multi-gradation mask which is an exposure mask in which transmitted light has a plurality of intensities. Good. A resist mask formed by using a multi-gradation mask has a shape having a plurality of film thicknesses, and the shape can be further deformed by etching, so that it can be used in a plurality of etching steps for processing different patterns. .. Therefore, it is possible to form a resist mask corresponding to at least two or more different patterns by using one multi-tone mask. Therefore, the number of exposure masks can be reduced, and the corresponding photolithography process can also be reduced, so that the process can be simplified.

It is desired to optimize the etching conditions so that the oxide semiconductor film 441 is not etched and divided when the conductive films used for the source electrode and the drain electrode are etched. However, it is difficult to obtain the condition that only the conductive film is etched and the oxide semiconductor film 441 is not etched at all, and the oxide semiconductor film 4 is etched when the conductive film is etched.
Only a part of 41 is etched to form an oxide semiconductor film having grooves (recesses).

In the present embodiment, a Ti film is used as the conductive film used for the source electrode and the drain electrode, and an In-Ga-Zn-O-based oxide semiconductor is used for the oxide semiconductor film 441. 31 wt% hydrogen peroxide solution: 28 wt% ammonia water: water = 5:
2: 2) is used.

Next, _{plasma treatment using a gas such as N 2} O, N ₂ , or Ar may be performed to remove hydrogen, water, and the like adhering to the surface of the exposed oxide semiconductor film. When the plasma treatment is performed, it is desirable to form the metal oxide film 407 in contact with a part of the oxide semiconductor film 441 without being exposed to the atmosphere following the plasma treatment.

Next, the source electrode 405a and the drain electrode 405b are covered, and the oxide semiconductor film 4 is used.
A metal oxide film 407 in contact with a part of 41 is formed (see FIG. 1C). The film thickness of the metal oxide film 407 is thicker than that of the oxide semiconductor film 441. The metal oxide film 407 is a film that comes into contact with the back channel side of the oxide semiconductor film 441, that is, the oxide semiconductor film 441 between the source electrode 405a and the drain electrode 405b, and removes the charge accumulated at the interface thereof.

Due to the electric charge accumulated in the source electrode 405a or the drain electrode 405b, the source electrode 40
Positive charges may move from the 5a or the drain electrode 405b to the oxide semiconductor film and charge the interface on the back channel side of the oxide semiconductor film. In particular, if the electrical conductivity of the oxide semiconductor film and the electrical conductivity of the material layer in contact with the back channel side of the oxide semiconductor film are different,
The electric charge flows to the oxide semiconductor film, the electric charge is captured at the interface, and is combined with hydrogen in the oxide semiconductor film to become a donor center at the interface. This causes a problem that the characteristics of the transistor fluctuate. Therefore, both reduction of hydrogen in the oxide semiconductor film and antistatic of the oxide semiconductor film are important.

The difference between the band gap of the oxide semiconductor film and the band gap of the metal oxide film is 3 eV.
Less than is preferable. For example, when an In-Ga-Zn-O oxide semiconductor is used as the oxide semiconductor film and silicon oxide or aluminum oxide is used as the metal oxide film, In-Ga-
Since the band gap of the Zn—O oxide semiconductor is 3.15 eV and the band gap of silicon oxide and aluminum oxide is 8 eV, the above-mentioned problems may occur. Also,
If a film containing a nitride (for example, a silicon nitride film) is used instead of the metal oxide film, the electrical conductivity of the oxide semiconductor film may fluctuate due to contact between the film containing the nitride and the oxide semiconductor film. There is.

Therefore, it is preferable that the metal oxide film 407 has a property of quickly removing even if a positive charge is charged on the back channel side of the oxide semiconductor film. However, the metal oxide film 407
The material used for is a material having a hydrogen content equal to or less than that of the oxide semiconductor film and not more than an order of magnitude more than the oxide semiconductor film, and its energy gap is oxidized. It is preferable that the material has equal to or more than the material of the material semiconductor film.

In one aspect of the invention, the metal oxide film is gallium oxide, such as gallium oxide (GaO).
A case where x (X> 0)) is used will be described. The physical properties of gallium oxide are, for example, a bandgap of 3.0 eV to 5.2 eV (for example, 4.9 eV), a dielectric constant of 8 to 20, an electron affinity of 3.5 eV, and In-Ga-Zn-O. The physical properties of the oxide semiconductor are, for example,
The band gap is 3.15 eV, the dielectric constant is 15, the electron affinity is 3.5 eV, and the difference in physical properties between gallium oxide and the In-Ga-Zn-O oxide semiconductor is small, which is preferable. Further, since gallium oxide has a wide band gap of about 4.9 eV, it has translucency in the visible light region. Further, it is preferable to use gallium oxide as the metal oxide film because the contact resistance between the In-Ga-Zn-O-based oxide semiconductor film and the gallium oxide film can be reduced. When gallium oxide is used as the metal oxide film, In
In addition to the −Ga—Zn—O-based oxide semiconductor, an In—Ga—O-based oxide semiconductor or a Ga—Zn—O-based oxide semiconductor may be used as the oxide semiconductor material.

As described above, by using the metal oxide film having an antistatic function, it is possible to suppress the accumulation of electric charges on the back channel side of the oxide semiconductor film. Further, by providing the metal oxide film on the upper surface of the oxide semiconductor film, even if the back channel side of the oxide semiconductor film is positively charged, it can be quickly removed. Further, by using the metal oxide film 407, it is possible to prevent the generation of parasitic channels on the back channel side of the oxide semiconductor film 403. As a result, fluctuations in electrical characteristics such as the electrical conductivity of the oxide semiconductor film can be suppressed, so that the reliability of the transistor can be improved.

It is preferable to use a gallium oxide film as the metal oxide film. The gallium oxide film can be obtained by a sputtering method, a CVD method, a vapor deposition method or the like. The gallium oxide film has a bandgap of about 4.9 eV and is translucent in the visible light region, although it depends on the composition ratio of oxygen and gallium.

In this specification, gallium oxide may be referred to as GaOx (x> 0). For example, Ga
When Ox has a crystal structure, Ga ₂ O ₃ with x = 1.5 is known.

In the present embodiment, as the metal oxide film 407, a gallium oxide film obtained by a sputtering method using a pulsed direct current (DC) power source is used. As the target used in the sputtering method, it is preferable to use a gallium oxide target. Further, indium or zinc may be appropriately added to the metal oxide film 407 according to the electric conductivity of the oxide semiconductor film to be used to adjust the electric conductivity. For example, a film containing 0.01 to 5 atomic% of indium or zinc is formed by a sputtering method using a target obtained by adding indium or zinc to gallium oxide. By adding indium or zinc, the electric conductivity of the metal oxide film 407 is improved and brought close to the electric conductivity of the oxide semiconductor film 403, so that the accumulation of electric charges can be further reduced.

In particular, when an In-Ga-Zn-O film is used as the oxide semiconductor film, the metal oxide film 40
It is preferable because it contains a gallium element common to GaOx used as No. 7 and has good compatibility with the materials.

The metal oxide film 407 is preferably formed by a method that does not allow impurities such as water and hydrogen to be mixed. When hydrogen is contained in the metal oxide film 407, the hydrogen penetrates into the oxide semiconductor film or oxygen is extracted from the oxide semiconductor film by hydrogen, and the back channel of the oxide semiconductor film becomes low resistance (n). It may be typed) and a parasitic channel may be formed. Therefore,
It is important that hydrogen is not used in the film forming method so that the metal oxide film 407 is a film containing as little hydrogen as possible.

In the present embodiment, a gallium oxide film having a film thickness of more than 10 nm and a film thickness of the oxide semiconductor film 441 or more is formed as the metal oxide film 407 by using a sputtering method. By making the thickness of the metal oxide film 407 thicker than that of the oxide semiconductor film 441 in this way, the metal oxide film 4
This is because 07 can efficiently remove the electric charge. The substrate temperature at the time of film formation may be room temperature or higher and 300 ° C. or lower. The film formation of the gallium oxide film by the sputtering method can be performed in a rare gas (typically argon) atmosphere, an oxygen atmosphere, or a mixed atmosphere of a rare gas and oxygen.

As in the case of film formation of the oxide semiconductor film, it is preferable to use an adsorption type vacuum pump (cryopump or the like) in order to remove residual moisture in the film formation chamber of the metal oxide film 407. The concentration of impurities contained in the metal oxide film 407 formed in the film forming chamber exhausted by using the cryopump can be reduced. Further, as an exhaust means for removing residual water in the film forming chamber of the metal oxide film 407, a turbo pump with a cold trap may be added.

As the sputter gas used for forming the metal oxide film 407, it is preferable to use a high-purity gas from which impurities such as hydrogen, water, hydroxyl groups and hydrides have been removed.

Further, the metal oxide film 407 is at least a channel forming region of the oxide semiconductor film, the source electrode 4
The 05a and the drain electrode 405b may be covered, and if necessary, the metal oxide film 407 may be selectively removed. For etching the gallium oxide film used in the present embodiment,
Known wet etching or known dry etching can be used. For example, wet etching is performed using a hydrofluoric acid solution or nitric acid.

Next, the oxide semiconductor film 441 is heat-treated in a state where the metal oxide film 407 and a part (channel forming region) are in contact with each other (see FIG. 1C).

The temperature of the heat treatment is 250 ° C. or higher and 650 ° C. or lower, preferably 450 ° C. or higher and 600 ° C. or lower.
Alternatively, it should be less than the distortion point of the substrate. For example, the substrate is introduced into an electric furnace, which is one of the heat treatment devices, and the oxide semiconductor film is heat-treated at 450 ° C. for 1 hour in a nitrogen atmosphere.

The heat treatment device is not limited to the electric furnace, and a device that heats the object to be treated by heat conduction or heat radiation from a heating element such as a resistance heating element may be used. For example, GRTA (Gas R)
apid Thermal Anneal) device, LRTA (Lamp Rapid T)
RTA (Rapid Thermal Anneal) such as a hermal Anneal device
al) A device can be used. The LRTA device is a device that heats an object to be processed by radiation of light (electromagnetic waves) emitted from lamps such as halogen lamps, metal halide lamps, xenon arc lamps, carbon arc lamps, high pressure sodium lamps, and high pressure mercury lamps. The GRTA device is a device that performs heat treatment using a high-temperature gas. For hot gas,
A rare gas such as argon or an inert gas such as nitrogen that does not react with the object to be treated by heat treatment is used. When the GRTA device is used as the heat treatment device, the substrate may be heated in an inert gas heated to a high temperature of 650 ° C. to 700 ° C. because the heat treatment time is short.

The heat treatment is nitrogen, oxygen, ultra-dry air (water content is 20 ppm or less, preferably 1 pp).
M or less, preferably 10 ppb or less air) or rare gas (argon, helium, etc.)
However, it is preferable that the atmosphere of nitrogen, oxygen, ultra-dry air, or rare gas does not contain water, hydrogen, or the like. Further, the purity of nitrogen, oxygen, or rare gas to be introduced into the heat treatment apparatus is 6N (99.99999%) or more, preferably 7N (99.99999%).
9%) or more (that is, the impurity concentration is 1 ppm or less, preferably 0.1 ppm or less).

Further, since the heat treatment is performed in a state where the oxide semiconductor film and the metal oxide film 407 containing oxygen are in contact with each other, it is one of the main component materials constituting the oxide semiconductor which is reduced at the same time by the removal process of impurities. Oxygen can be supplied from the metal oxide film 407 containing oxygen to the oxide semiconductor film. Thereby, the charge capture center in the oxide semiconductor film can be reduced. Through the above steps, a highly purified and electrically i-type (intrinsic) oxide semiconductor film 403 is obtained.
Further, by this heat treatment, impurities can be removed from the metal oxide film 407 at the same time to improve the purity.

In the highly purified oxide semiconductor film 403, there are very few carriers derived from the donor, and there are very few carriers.
The carrier concentration is ^{less than 1 × 10 14} / cm ³ , preferably less than 1 × 10 ¹² / cm ³ , and more preferably less than 1 × 10 ¹¹ / cm ³ .

The transistor 410 is formed by the above steps (see FIG. 1 (D)). Transistor 410
Is a transistor containing an oxide semiconductor film 403 that has been purified by intentionally removing impurities such as hydrogen, water, hydroxyl groups, and hydrides (also referred to as hydrides) from the oxide semiconductor film. Therefore, the transistor 410 is electrically stable because the fluctuation of the electrical characteristics is suppressed.

Further, in addition to the above heat treatment, another heat treatment may be performed. For example, oxide semiconductor film 4
After forming 41, heat treatment (first heat treatment) may be performed, and after forming the metal oxide film 407, further heat treatment (second heat treatment) may be performed. In this case, the first heat treatment can be, for example, a treatment in which heating is performed in an atmosphere of an inert gas and cooling is performed in an atmosphere of oxygen (at least in an atmosphere containing oxygen). By applying such a first heat treatment, dehydration and oxidation of the oxide semiconductor film can be suitably performed.

Further, the heat treatment may be further performed after the second heat treatment. For example, 100 in the atmosphere
The heat treatment may be carried out at ° C. or higher and 200 ° C. or lower for 1 hour or longer and 30 hours or lower. This heat treatment may be carried out while maintaining a constant heating temperature, or the temperature may be raised from room temperature to a heating temperature of 100 ° C. or higher and 200 ° C. or lower, and the temperature may be lowered from the heating temperature to room temperature a plurality of times. You may.

Further, since the transistor 410 using the oxide semiconductor film 403 can obtain a relatively high field effect mobility, it can be driven at high speed. Therefore, by using the above-mentioned transistor in the pixel portion, it is possible to provide a high-quality image. Further, since the drive circuit portion and the pixel portion having the transistor including the highly purified oxide semiconductor film can be formed on the same substrate, the number of parts of the semiconductor device can be reduced.

Further, in the transistor 410 having the metal oxide film 407, it is possible to prevent the generation of parasitic channels on the back channel side of the oxide semiconductor film 403. Furthermore, the transistor 41
By preventing the generation of parasitic channels on the back channel side of the oxide semiconductor film 403 at 0, fluctuations in the threshold voltage can be suppressed, so that a transistor with improved reliability can be obtained.

By the way, in the transistor 410 shown in FIG. 1 (D), the oxide semiconductor film 403 and
Two layers of dielectrics are in contact with the metal oxide film 407. When two different layers of dielectrics are laminated, the dielectric constant of the first layer (oxide semiconductor film 403 in the transistor 410) is ε ₁ , the conductivity is σ ₁ , and the thickness is d ₁ , and the second layer ( In the transistor 410, when the dielectric constant of the metal oxide film 407) is ε ₂ , the conductivity is σ ₂ , and the thickness is d ₂ , the lamination of the two layers is shown in FIG. 9 (
It can be represented by the model diagram of A). In FIG. 9A, S represents an area. Further, the model diagram of FIG. 9A can be replaced with the equivalent circuit of FIG. 9B. C in the figure
₁ represents the capacitance value of the _{first layer, G 1} represents the resistance value of the first layer, C ₂ represents the capacitance value of the _{second layer, and G 2} represents the resistance value of the second layer. Here, when a voltage V is applied to the two layers, it is said that the electric charge Q represented by the following equation (1) is accumulated at the interface between the two layers after t seconds.

In the transistor 410 shown in FIG. 1 (D), the interface on which the above-mentioned charge Q is accumulated corresponds to the back channel side of the oxide semiconductor film 403, and the dielectric constant or electrical conductivity of the metal oxide film 407, or metal oxidation. By appropriately setting the film thickness of the film 407, the charge Q accumulated at the interface on the back channel side can be reduced.

Here, when the equation (1) is modified, it is represented by the following equations (2) and (3).

From the formulas (2) and (3), in order to reduce the charge Q, the following four conditions (A) to (D) can be assumed.
Condition (A) Make τ _i very large.
Condition (B) Brings V ₂ closer to zero, i.e. makes G ₂ much larger than _{G 1.}
Condition (C) _{Bring C 2} closer to zero.
Condition (D) Brings τ ₁ closer to τ _2.

In condition (A), in order to make _{τ i very large, τ i} = (C ₁ + C ₂ ) / (G ₁ + G ₂₎
), Therefore, (C ₁ + C ₂ ) may be made much larger than (G ₁ + G _2). here,
Since C ₁ and G ₁ are parameters of the oxide semiconductor film 403, it is necessary to increase _{C 2 in} order to reduce the charge Q by the metal oxide film 407. However, C ₂ = ε ₂
When the _{C 2} greater than S / _{d 2} at epsilon _2, Q becomes larger than the formula (2), resulting in inconsistency. In other words it is not possible to adjust the charge Q at τ _i.

_{In order to bring V 2} closer to zero under the condition (B) _{, G 2} >> G ₁ should be satisfied from the equation (3). Since G ₁ is a parameter of the oxide semiconductor film 403, it is necessary to increase _{G 2 in order to reduce the charge Q by the metal oxide film 407.} Specifically, G ₂ = σ ₂ S
Since it is / d _2, it is necessary to select a material in which _{d 2} is small or σ _{2 is large.} However, reduction of _{d 2} is, _{C 2} = _{C 2} is larger than epsilon ₂ S / _{d 2,} can not be employed conditions (A) and likewise for Q increases. Further, when σ ₂ is large, it means that the metal oxide film 407 has higher electrical conductivity than the oxide semiconductor film 403, and cannot be adopted because there is a high risk of leakage current generation and short circuit.

In the condition (C), in order to very small _{C 2,} from _{C 2 = ε 2 S / d} 2, either by increasing _{d 2,} and thus to select a material with a low epsilon _2.

Further, the condition (D), in order to approximate the tau ₁ to tau _{2 is, τ 1 = ε 1 / σ} 1, τ 2 = ε 2 /
Since it is _{σ 2 , a film having ε 1} / σ ₁ ≈ ε ₂ / σ ₂ may be selected. This is C ₁ / G ₁ ≒ C
Equivalent to ₂ / G _2.

Therefore, in order to effectively prevent the accumulation of electric charge Q, the film thickness of the metal oxide film 407 (d _{2)
) Is increased, or a material having a small dielectric constant (ε 2} ), preferably a material smaller than the oxide semiconductor film 403 (for example, a material having a dielectric constant ε of 8 or more and 20 or less) is selected as the material of the metal oxide film 407. It is preferable to do so. Alternatively, a material having similar physical properties to the oxide semiconductor film is used as a metal so that _{ε 1} / σ ₁ ≈ ε ₂ / σ ₂ (ε ₁ is the permittivity of the oxide semiconductor and σ _{1 is the conductivity of the oxide semiconductor).} It is preferably selected as an oxide film.

As described above, in the transistor 410 having the metal oxide film 407 having an antistatic function,
It is possible to suppress the accumulation of electric charges on the back channel side of the oxide semiconductor film. Further, by providing the metal oxide film on the upper surface of the oxide semiconductor film, even if the back channel side of the oxide semiconductor film is positively charged, it can be quickly removed. In addition, metal oxide film 407
In the transistor 410 having the above, it is possible to prevent the generation of parasitic channels on the back channel side of the oxide semiconductor film 403. Further, by preventing the generation of parasitic channels on the back channel side of the oxide semiconductor film in the transistor, fluctuations in the threshold voltage can be suppressed. As a result, fluctuations in the electrical conductivity and the like of the oxide semiconductor film can be suppressed, so that the reliability of the transistor can be improved.

As described above, it is possible to provide a semiconductor device using an oxide semiconductor having stable electrical characteristics. Therefore, it is possible to provide a highly reliable semiconductor device.

As described above, the configurations and methods shown in the present embodiment can be appropriately combined with the configurations and methods shown in other embodiments.

(Embodiment 2)
In this embodiment, another embodiment of the method for manufacturing a semiconductor device will be described. The same part or the part having the same function as the above-described embodiment and the steps can be performed in the same manner as in the above-described embodiment, and the repeated description will be omitted. Further, detailed description of the same part will be omitted.

In the present embodiment, in the method for manufacturing the transistor 410 shown in the first embodiment, an example in which the oxide semiconductor film is heat-treated before forming the metal oxide film 407 in contact with the oxide semiconductor film is shown.

This heat treatment may be applied to the oxide semiconductor film before processing the island-shaped oxide semiconductor film after the oxide semiconductor film is formed and before the metal oxide film 407 is formed. Source electrode 4
It may be applied either before or after the formation of 05a and the drain electrode 405b.

The temperature of the heat treatment is 250 ° C. or higher and 650 ° C. or lower, preferably 450 ° C. or higher and 600 ° C. or lower. For example, the substrate is introduced into an electric furnace, which is one of the heat treatment devices, and the oxide semiconductor film is heat-treated at 450 ° C. for 1 hour in a nitrogen atmosphere. After the heat treatment, it is preferable to form a metal oxide film without contacting the atmosphere to prevent re-mixing of water or hydrogen into the oxide semiconductor film.

The heat treatment device is not limited to the electric furnace, and a device that heats the object to be treated by heat conduction or heat radiation from a heating element such as a resistance heating element may be used. For example, GRTA device, LRT
An RTA device such as the A device can be used. When the GRTA device is used as the heat treatment device, the substrate may be heated in an inert gas heated to a high temperature of 650 ° C. to 700 ° C. because the heat treatment time is short.

The heat treatment is nitrogen, oxygen, ultra-dry air (water content is 20 ppm or less, preferably 1 pp).
M or less, preferably 10 ppb or less air) or rare gas (argon, helium, etc.)
However, it is preferable that the atmosphere of nitrogen, oxygen, ultra-dry air, or rare gas does not contain water, hydrogen, or the like. Further, the purity of nitrogen, oxygen, or rare gas to be introduced into the heat treatment apparatus is 6N (99.99999%) or more, preferably 7N (99.99999%).
%) Or more (that is, the impurity concentration is 1 ppm or less, preferably 0.1 ppm or less).

By this heat treatment, impurities such as water and hydrogen in the oxide semiconductor film can be reduced.

Further, it is one of the main component materials constituting the oxide semiconductor, which is reduced at the same time by the removal process of impurities by performing the heat treatment in the state where the oxide semiconductor film and the metal oxide film containing oxygen are in contact with each other. Oxygen can be supplied to the oxide semiconductor film from the metal oxide film containing oxygen.

Therefore, if the oxide semiconductor film is heat-treated before the formation of the metal oxide film and the heat treatment after the formation of the metal oxide film, impurities such as water and hydrogen are further desorbed. An oxide semiconductor film as close as possible to an intrinsic semiconductor) or i-type can be obtained.

Therefore, the transistor containing the highly purified oxide semiconductor film is electrically stable because the fluctuation of the electrical characteristics is suppressed.

Further, the transistor having a metal oxide film can prevent the generation of parasitic channels on the back channel side of the oxide semiconductor film.

As described above, it is possible to provide a semiconductor device using an oxide semiconductor having stable electrical characteristics. Therefore, it is possible to provide a highly reliable semiconductor device.

As described above, the configurations and methods shown in the present embodiment can be appropriately combined with the configurations and methods shown in other embodiments.

(Embodiment 3)
A semiconductor device (also referred to as a display device) having a display function can be manufactured by using the transistor shown as an example in any one of the first and second embodiments. Further, a part or the whole of the drive circuit including the transistor can be integrally formed on the same substrate as the pixel portion to form a system on panel.

In FIG. 2A, a sealing material 4005 is provided so as to surround the pixel portion 4002 provided on the first substrate 4001, and is sealed by the second substrate 4006. Figure 2 (
In A), a scanning line drive formed of a single crystal semiconductor film or a polycrystalline semiconductor film on a separately prepared substrate in a region different from the region surrounded by the sealing material 4005 on the first substrate 4001. A circuit 4004 and a signal line drive circuit 4003 are mounted. Further, various signals and potentials given to the separately formed signal line drive circuit 4003 and the scanning line drive circuit 4004 or the pixel unit 4002 are obtained by FPC (Flexible printed circuit board).
) 4018a, 4018b.

In FIGS. 2B and 2C, the pixel portion 4002 provided on the first substrate 4001.
And the scanning line drive circuit 4004, the sealing material 4005 is provided so as to surround the scanning line drive circuit 4004.
Further, a second substrate 4006 is provided on the pixel unit 4002 and the scanning line drive circuit 4004. Therefore, the pixel portion 4002 and the scanning line drive circuit 4004 are sealed together with the display element by the first substrate 4001, the sealing material 4005, and the second substrate 4006. Figure 2
In (B) and FIG. 2C, a single crystal semiconductor film or a polycrystalline semiconductor film is formed on a separately prepared substrate in a region different from the region surrounded by the sealing material 4005 on the first substrate 4001. The signal line drive circuit 4003 formed by the above is mounted. 2 (B) and 2 (C)
In), various signals and potentials given to the separately formed signal line drive circuit 4003 and the scanning line drive circuit 4004 or the pixel unit 4002 are supplied from the FPC 4018.

Further, in FIGS. 2 (B) and 2 (C), a signal line drive circuit 4003 is separately formed, and the first signal line drive circuit 4003 is formed.
Although an example of mounting on the substrate 4001 of the above is shown, the present invention is not limited to this configuration. The scanning line drive circuit may be separately formed and mounted, or only a part of the signal line driving circuit or a part of the scanning line driving circuit may be separately formed and mounted.

The method of connecting the separately formed drive circuit is not particularly limited, and COG (Ch) is not particularly limited.
ip On Glass) method, wire bonding method, or TAB (Tape A)
An automated Bonding) method or the like can be used. FIG. 2 (A) shows C
This is an example of mounting the signal line drive circuit 4003 and the scanning line drive circuit 4004 by the OG method.
FIG. 2B is an example of mounting the signal line drive circuit 4003 by the COG method, and FIG. 2C is shown in FIG. 2C.
) Is an example of mounting the signal line drive circuit 4003 by the TAB method.

Further, the display device includes a panel in which the display element is sealed, and a module in which an IC or the like including a controller is mounted on the panel.

The display device in the present specification refers to an image display device, a display device, or a light source (including a lighting device). In addition, an IC (integrated circuit) is directly mounted on a connector, for example, a module to which FPC or TAB tape or TCP is attached, a module having a printed wiring board at the end of TAB tape or TCP, or a display element by the COG method. All modules shall be included in the display device.

Further, the pixel portion and the scanning line drive circuit provided on the first substrate 4001 have a plurality of transistors, and the transistor shown as an example in either the first or second embodiment can be applied.

The display elements provided in the display device include a liquid crystal element (also referred to as a liquid crystal display element) and a light emitting element (also called a liquid crystal display element).
(Also referred to as a light emitting display element), can be used. The light emitting element includes an element whose brightness is controlled by current or voltage in its category, and specifically, an inorganic EL (Electro).
Luminescence), organic EL and the like are included. Further, a display medium whose contrast changes due to an electric action, such as electronic ink, can also be applied.

A form of the semiconductor device will be described with reference to FIGS. 3 to 5. 3 to 5 are shown in FIG. 2 (
B) corresponds to the cross-sectional view taken along the line MN.

As shown in FIGS. 3 to 5, the semiconductor device has a connection terminal electrode 4015 and a terminal electrode 4016, and the connection terminal electrode 4015 and the terminal electrode 4016 pass through the terminal of the FPC 4018 and the anisotropic conductive film 4019. , Electrically connected.

The connection terminal electrode 4015 is formed of the same conductive film as the first electrode layer 4030, and the terminal electrode 4
016 is formed of the same conductive film as the source electrode and drain electrode of the transistors 4010 and 4011.

Further, the pixel unit 4002 provided on the first substrate 4001 and the scanning line drive circuit 4004
A plurality of transistors are provided, and FIGS. 3 to 5 illustrate the transistor 4010 included in the pixel unit 4002 and the transistor 4011 included in the scanning line drive circuit 4004. In FIG. 3, a metal oxide film 4020 having an antistatic function is provided on the transistors 4010 and 4011, and in FIGS. 4 and 5, an insulating layer 4021 is further provided. The insulating film 4023 is an insulating film that functions as a base film.

In the present embodiment, the transistor 4010 and the transistor 4011 are used as the first embodiment.
Alternatively, the transistor shown in any of 2 can be applied.

In the transistor 4010 and the transistor 4011, the oxide semiconductor film is subjected to heat treatment after forming the metal oxide film 4020 laminated on the oxide semiconductor film, thereby performing impurities such as hydrogen, water, hydroxyl groups or hydrides (also referred to as hydrides). Is a high-purity oxide semiconductor film that is intentionally excluded from the oxide semiconductor film.

Further, since the heat treatment is performed in a state where the oxide semiconductor film and the metal oxide film 4020 containing oxygen are in contact with each other, it is one of the main component materials constituting the oxide semiconductor which is reduced at the same time by the removal process of impurities. Oxygen can be supplied to the oxide semiconductor film from the metal oxide film 4020 containing oxygen. Therefore, the oxide semiconductor film is made more pure and electrically made i-type (intrinsic).

Therefore, the transistor 4010 and the transistor 4 containing the highly purified oxide semiconductor film
In 011 the fluctuation of electrical characteristics is suppressed and it is electrically stable. Therefore, it is possible to provide a highly reliable semiconductor device as the semiconductor device of the present embodiment shown in FIGS. 3 to 5.

Further, the transistor having a metal oxide film having an antistatic function can prevent the generation of parasitic channels on the back channel side of the oxide semiconductor film. Further, by preventing the generation of parasitic channels on the back channel side of the oxide semiconductor film in the transistor, fluctuations in the threshold voltage can be suppressed.

Further, in the present embodiment, a conductive layer may be provided on the metal oxide film at a position overlapping the channel formation region of the oxide semiconductor film of the transistor 4011 for the drive circuit. By providing the conductive layer at a position overlapping the channel forming region of the oxide semiconductor film, the amount of change in the threshold voltage of the transistor 4011 before and after the BT test can be further reduced. Also,
The potential of the conductive layer may be the same as or different from that of the gate electrode of the transistor 4011, and may function as a second gate electrode. In addition, the potential of the conductive layer is GND,
It may be 0V or a floating state.

Further, the conductive layer also has a function of shielding an external electric field, that is, a function of preventing the external electric field from acting on the inside (circuit portion including a thin film transistor) (particularly, an electrostatic shielding function against static electricity). The shielding function of the conductive layer can prevent the electrical characteristics of the transistor from fluctuating due to the influence of an external electric field such as static electricity.

The transistor 4010 provided in the pixel unit 4002 is electrically connected to the display element to form a display panel. The display element is not particularly limited as long as it can display, and various display elements can be used.

FIG. 3 shows an example of a liquid crystal display device using a liquid crystal element as a display element. In FIG. 3, the liquid crystal element 4013, which is a display element, includes a first electrode layer 4030, a second electrode layer 4031, and a liquid crystal layer 4008. An insulating film 4032 and an insulating film 4033 that function as an alignment film are provided so as to sandwich the liquid crystal layer 4008. The second electrode layer 4031 is the second substrate 400.
It is provided on the 6th side, and the first electrode layer 4030 and the second electrode layer 4031 are laminated via the liquid crystal layer 4008.

Further, 4035 is a columnar spacer obtained by selectively etching the insulating film.
It is provided to control the film thickness (cell gap) of the liquid crystal layer 4008. A spherical spacer may be used.

When a liquid crystal element is used as the display element, a thermotropic liquid crystal, a low molecular weight liquid crystal, a polymer liquid crystal, a polymer dispersed liquid crystal, a strong dielectric liquid crystal, an anti-strong dielectric liquid crystal, or the like can be used. Depending on the conditions, these liquid crystal materials exhibit a cholesteric phase, a smectic phase, a cubic phase, a chiral nematic phase, an isotropic phase and the like.

Further, a liquid crystal showing a blue phase without using an alignment film may be used. The blue phase is one of the liquid crystal phases, and is a phase that appears immediately before the transition from the cholesteric phase to the isotropic phase when the temperature of the cholesteric liquid crystal is raised. Since the blue phase is expressed only in a narrow temperature range, a liquid crystal composition mixed with 5% by weight or more of a chiral agent is used for the liquid crystal layer in order to improve the temperature range.
A liquid crystal composition containing a liquid crystal exhibiting a blue phase and a chiral agent has a short response speed of 1 msec or less, is optically isotropic, does not require an orientation treatment, and has a small viewing angle dependence. Further, since it is not necessary to provide an alignment film, the rubbing process is not required, so that electrostatic breakdown caused by the rubbing process can be prevented, and defects and breakage of the liquid crystal display device during the manufacturing process can be reduced. .. Therefore, it is possible to improve the productivity of the liquid crystal display device. A transistor using an oxide semiconductor film may deviate from the design range due to a significant change in the electrical characteristics of the transistor due to the influence of static electricity. Therefore, it is more effective to use a blue phase liquid crystal material for a liquid crystal display device having a transistor using an oxide semiconductor film.

The resistivity of the liquid crystal material is 1 × 10 ⁹ Ω · cm or more, preferably 1 × 10 ^{1
It is 1} Ω · cm or more, more preferably 1 × 10 ¹² Ω · cm or more. The value of the resistivity in the present specification is a value measured at 20 ° C.

The size of the holding capacitance provided in the liquid crystal display device is set so that the electric charge can be held for a predetermined period in consideration of the leakage current of the transistor arranged in the pixel portion and the like. By using a transistor having a high-purity oxide semiconductor film, it is sufficient to provide a holding capacity having a capacity of 1/3 or less, preferably 1/5 or less of the liquid crystal capacity of each pixel. ..

The transistor using the highly purified oxide semiconductor film used in the present embodiment can reduce the current value (off current value) in the off state. Therefore, the holding time of an electric signal such as an image signal can be lengthened, and the writing interval can be set long when the power is on. Therefore, the frequency of the refresh operation can be reduced, which has the effect of suppressing power consumption.

Further, the transistor using the highly purified oxide semiconductor film used in the present embodiment can be driven at high speed because a relatively high field effect mobility can be obtained. Therefore, by using the above-mentioned transistor in the pixel portion of the liquid crystal display device, it is possible to provide a high-quality image. Further, since the drive circuit portion having the transistor and the pixel portion can be formed on the same substrate, the number of parts of the liquid crystal display device can be reduced.

The liquid crystal display device has a TN (Twisted Nematic) mode and an IPS (In-P).
lane-Switching mode, FFS (Fringe Field SWit)
ching) mode, ASM (Axially Symmetrically identified)
Micro-cell mode, OCB (Optical Compensated B)
irrefringence mode, FLC (Ferroelectric Liquid Liqui)
d Crystal) mode, AFLC (Antiferroelectric Liq)
A uid Crystal) mode or the like can be used.

Further, a normally black type liquid crystal display device, for example, a transmissive type liquid crystal display device adopting a vertical orientation (VA) mode may be used. Here, the vertical orientation mode is a type of method for controlling the arrangement of liquid crystal molecules on the liquid crystal display panel, and is a method in which the liquid crystal molecules face the panel surface in the direction perpendicular to the panel surface when no voltage is applied. There are several vertical orientation modes, for example, MVA (Multi-Domain Vertical Alignme).
nt) mode, PVA (Patterned Vertical Alignment)
Mode, ASV mode and the like can be used. Further, it is possible to use a method called multi-domain or multi-domain design, in which pixels are divided into several regions (sub-pixels) and molecules are tilted in different directions.

Further, in the display device, an optical member (optical substrate) such as a black matrix (light-shielding layer), a polarizing member, a retardation member, and an antireflection member is appropriately provided. For example, circularly polarized light using a polarizing substrate and a retardation substrate may be used. Further, a backlight, a side light or the like may be used as the light source.

It is also possible to use a plurality of light emitting diodes (LEDs) as a backlight to perform a time division display method (field sequential drive method). By applying the field sequential drive method, color display can be performed without using a color filter.

Further, as the display method in the pixel unit, a progressive method, an interlaced method, or the like can be used. Further, the color elements controlled by the pixels at the time of color display are not limited to the three colors of RGB (R represents red, G represents green, and B represents blue). For example, RGBW (W stands for white)
, Or RGB with one or more colors such as yellow, cyan, and magenta added. In addition, it should be noted.
The size of the display area may be different for each dot of the color element. However, the present embodiment is not limited to the display device for color display, and can be applied to the display device for monochrome display.

Further, as a display element included in the display device, a light emitting element using electroluminescence can be applied. Light emitting devices that utilize electroluminescence are distinguished by whether the light emitting material is an organic compound or an inorganic compound. Generally, the former is organic E.
The L element and the latter are called inorganic EL elements.

In the organic EL element, by applying a voltage to the light emitting element, electrons and holes are injected into the layer containing the luminescent organic compound from the pair of electrodes, respectively, and a current flows. Then, when those carriers (electrons and holes) are recombined, the luminescent organic compound forms an excited state, and when the excited state returns to the ground state, it emits light. From such a mechanism, such a light emitting element is called a current excitation type light emitting element.

The inorganic EL element is classified into a dispersed inorganic EL element and a thin film type inorganic EL element according to the element configuration. The dispersed inorganic EL element has a light emitting layer in which particles of a light emitting material are dispersed in a binder, and the light emitting mechanism is donor-acceptor recombination type light emission utilizing a donor level and an acceptor level. In the thin film type inorganic EL element, the light emitting layer is sandwiched between the dielectric layers, and the light emitting layer is sandwiched between the dielectric layers.
Furthermore, it has a structure in which it is sandwiched between electrodes, and the light emission mechanism is localized light emission that utilizes the inner-shell electronic transition of metal ions. Here, a case where an organic EL element is used as the light emitting element will be described.

The light emitting element may have at least one of a pair of electrodes transparent in order to extract light. Then, a transistor and a light emitting element are formed on the substrate, and the top surface injection that extracts light emission from the surface opposite to the substrate, the bottom surface injection that extracts light emission from the surface on the substrate side, and the surface on the substrate side and the surface opposite to the substrate. There is a light emitting element having a double-sided injection structure that extracts light from the light emitting device, and any light emitting element having an injection structure can be applied.

FIG. 4 shows an example of a light emitting device using a light emitting element as a display element. Light emitting element 4 which is a display element
The 513 is electrically connected to the transistor 4010 provided in the pixel unit 4002.
The configuration of the light emitting element 4513 is a laminated structure of the first electrode layer 4030, the electroluminescent layer 4511, and the second electrode layer 4031, but is not limited to the configuration shown. The configuration of the light emitting element 4513 can be appropriately changed according to the direction of the light extracted from the light emitting element 4513 and the like.

The partition wall 4510 is formed by using an organic insulating material or an inorganic insulating material. In particular, it is preferable to use a photosensitive resin material to form an opening on the first electrode layer 4030 so that the side wall of the opening becomes an inclined surface formed with a continuous curvature.

The electroluminescent layer 4511 may be composed of a single layer or may be configured such that a plurality of layers are laminated.

A protective film may be formed on the second electrode layer 4031 and the partition wall 4510 so that oxygen, hydrogen, water, carbon dioxide, etc. do not enter the light emitting element 4513. As the protective film, a silicon nitride film, a silicon oxide film, a DLC film, or the like can be formed. Also, the first substrate 400
Filler 45 in the space sealed by the first, second substrate 4006, and sealing material 4005.
14 is provided and sealed. As described above, it is preferable to package (enclose) with a protective film (bonded film, ultraviolet curable resin film, etc.) or a cover material having high airtightness and little degassing so as not to be exposed to the outside air.

As the filler 4514, in addition to an inert gas such as nitrogen or argon, an ultraviolet curable resin or a thermosetting resin can be used, and PVC (polyvinyl chloride), acrylic, polyimide, epoxy resin, silicone resin, PVB (polyvinyl) can be used. Butyral) or EVA (ethylene vinyl acetate) can be used. For example, nitrogen may be used as the filler.

If necessary, a polarizing plate or a circular polarizing plate (including an elliptical polarizing plate) is provided on the injection surface of the light emitting element.
An optical film such as a retardation plate (λ / 4 plate, λ / 2 plate) or a color filter may be appropriately provided. Further, an antireflection film may be provided on the polarizing plate or the circular polarizing plate. For example, it is possible to apply an anti-glare treatment that can diffuse the reflected light due to the unevenness of the surface and reduce the reflection.

Further, as a display device, it is also possible to provide electronic paper for driving electronic ink. Electronic paper is also called an electrophoresis display device (electrophoresis display), and has the advantages of being as easy to read as paper, having lower power consumption than other display devices, and being able to have a thin and light shape. ing.

The electrophoretic display device may have various forms, but a plurality of microcapsules containing a first particle having a positive charge and a second particle having a negative charge are dispersed in a solvent or a solute. By applying an electric field to the microcapsules, the particles in the microcapsules are moved in opposite directions and only the color of the particles aggregated on one side is displayed. The first particle or the second particle contains a dye and does not move in the absence of an electric field. Further, the color of the first particle and the color of the second particle are different (including colorless).

As described above, the electrophoresis display device is a display utilizing the so-called dielectrophoretic effect in which a substance having a high dielectric constant moves to an electric field region having a high dielectric constant.

The microcapsules dispersed in a solvent are called electronic inks, and the electronic inks can be printed on the surface of glass, plastic, cloth, paper, or the like. In addition, color display is also possible by using a color filter or particles having a dye.

The first particles and the second particles in the microcapsules are a conductor material, an insulator material, and the like.
A semiconductor material, a magnetic material, a liquid crystal material, a ferroelectric material, an electroluminescent material, an electrochromic material, a kind of material selected from a magnetic migration material, or a composite material thereof may be used.

Further, as the electronic paper, a display device using a twist ball display method can also be applied. In the twist ball display method, spherical particles painted in white and black are arranged between a first electrode layer and a second electrode layer, which are electrode layers used for a display element, and the first electrode layer and the first electrode layer are arranged. This is a method of displaying by controlling the orientation of spherical particles by causing a potential difference in the electrode layer of 2.

FIG. 5 shows an active matrix type electronic paper as a form of a semiconductor device. Figure 5
The electronic paper is an example of a display device using a twist ball display method.

A black region 4615a and a white region 4615b are provided between the first electrode layer 4030 connected to the transistor 4010 and the second electrode layer 4031 provided on the second substrate 4006, and the surrounding areas are filled with liquid. Spherical particles 4613 including the cavity 4612 are provided, and the periphery of the spherical particles 4613 is filled with a filler 4614 such as a resin. The second electrode layer 4031 corresponds to a common electrode (counter electrode). The second electrode layer 4031 is electrically connected to the common potential line.

In FIGS. 3 to 5, as the first substrate 4001 and the second substrate 4006, a flexible substrate can be used in addition to the glass substrate. For example, a translucent plastic substrate or the like can be used. Can be used. As plastic, FRP (Fiberglass)
s-Reinforced Plastics) board, PVF (polyvinyl fluoride)
A film, a polyester film or an acrylic resin film can be used. Further, a sheet having a structure in which an aluminum foil is sandwiched between a PVC film or a polyester film can also be used.

Further, the metal oxide film 4020 not only prevents the generation of parasitic channels on the back channel side of the oxide semiconductor film, but also simultaneously reduces the oxide semiconductor film from the oxide semiconductor film by the step of removing impurities such as hydrogen, water, hydroxyl group or hydride. It also has a function of supplying oxygen to the oxide semiconductor film.

As the metal oxide film 4020, a gallium oxide film formed by a sputtering method may be used. Further, a film obtained by adding indium or zinc to gallium oxide may be used, and for example, a gallium oxide film containing 0.01 to 5 atomic% of indium or zinc can be used. By adding indium or zinc, the electrical conductivity of the metal oxide film 4020 can be improved and the charge accumulation can be further reduced.

Further, the insulating layer 4021 can be formed by using an inorganic insulating material or an organic insulating material. When an organic insulating material having heat resistance such as acrylic resin, polyimide, benzocyclobutene resin, polyamide, and epoxy resin is used, it is suitable as a flattening insulating film. In addition to the above organic insulating materials, low dielectric constant materials (low-k materials), siloxane-based resins, and PSG
(Phosphorus glass), BPSG (Phosphoron glass) and the like can be used. An insulating layer may be formed by laminating a plurality of insulating films formed of these materials.

The method for forming the insulating layer 4021 is not particularly limited, and depending on the material, a sputtering method, a spin coating method, a dipping method, a spray coating method, a droplet ejection method (inkjet method, screen printing, offset printing, etc.), a roll coating method, etc. , Curtain coating, knife coating and the like can be used.

The display device transmits light from a light source or a display element to perform display. Therefore, all the thin films such as the substrate, the insulating film, and the conductive film provided in the pixel portion through which light is transmitted are made translucent with respect to light in the wavelength region of visible light.

In the first electrode layer 4030 and the second electrode layer 4031 (also referred to as a pixel electrode layer, a common electrode layer, a counter electrode layer, etc.) that apply a voltage to the display element, the direction of the light to be taken out and the place where the electrode layer is provided. , And the translucency and the reflectivity may be selected according to the pattern structure of the electrode layer.

The first electrode layer 4030 and the second electrode layer 4031 are indium oxide containing tungsten oxide, indium zinc oxide containing tungsten oxide, indium oxide containing titanium oxide, indium tin oxide containing titanium oxide, and indium. Tin oxide (hereinafter referred to as ITO).
), Indium zinc oxide, indium tin oxide to which silicon oxide is added, and other conductive materials having translucency can be used.

Further, the first electrode layer 4030 and the second electrode layer 4031 are tungsten (W), molybdenum (Mo), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (N).
b), Tantalum (Ta), Chromium (Cr), Cobalt (Co), Nickel (Ni), Titanium (Ti), Platinum (Pt), Aluminum (Al), Copper (Cu), Silver (Ag) and other metals ,
Alternatively, it can be formed from one or more of the alloys thereof or the nitrides thereof.

Further, the first electrode layer 4030 and the second electrode layer 4031 can be formed by using a conductive composition containing a conductive polymer (also referred to as a conductive polymer). As the conductive polymer, a so-called π-electron conjugated conductive polymer can be used. Examples thereof include polyaniline or a derivative thereof, polypyrrole or a derivative thereof, polythiophene or a derivative thereof, or a copolymer consisting of two or more kinds of aniline, pyrrole and thiophene or a derivative thereof.

Further, since the transistor is easily destroyed by static electricity or the like, it is preferable to provide a protection circuit for protecting the drive circuit. The protection circuit is preferably configured by using a non-linear element.

By applying the transistor shown in the first or second embodiment as described above, it is possible to provide a semiconductor device having various functions.

(Embodiment 4)
Using the transistor shown as an example in any one of the first and second embodiments, a semiconductor device having an image sensor function for reading information on an object can be manufactured.

FIG. 6A shows an example of a semiconductor device having an image sensor function. FIG. 6A is an equivalent circuit of a photosensor, and FIG. 6B is a cross-sectional view showing a part of the photosensor.

In the photodiode 602, one electrode is electrically connected to the photodiode reset signal line 658, and the other electrode is electrically connected to the gate of the transistor 640. Transistor 640
Is electrically connected to one of the source or drain to the photosensor reference signal line 672 and the other of the source or drain to one of the source or drain of the transistor 656. The transistor 656 is electrically connected to the gate signal line 659 at the gate and to the photosensor output signal line 671 at the other end of the source or drain.

In the circuit diagram of the present specification, "OS" is described as the symbol of the transistor using the oxide semiconductor film so that it can be clearly identified as the transistor using the oxide semiconductor film. In FIG. 6A, the transistor 640 and the transistor 656 are transistors using an oxide semiconductor film.

FIG. 6B is a cross-sectional view showing a photodiode 602 and a transistor 640 in a photosensor, in which a photodiode 602 and a transistor 640 functioning as a sensor are provided on a substrate 601 (TFT substrate) having an insulating surface. There is. A substrate 613 is provided on the photodiode 602 and the transistor 640 by using an adhesive layer 608.

On the transistor 640, a metal oxide film 631 having an antistatic function, an interlayer insulating layer 633,
An interlayer insulating layer 634 is provided. The photodiode 602 is provided on the interlayer insulating layer 633, and is provided between the electrode layer 641 formed on the interlayer insulating layer 633 and the electrode layer 642 provided on the interlayer insulating layer 634 from the interlayer insulating layer 633 side. It has a structure in which a first semiconductor layer 606a, a second semiconductor layer 606b, and a third semiconductor layer 606c are laminated in this order.

In the transistor 640, the oxide semiconductor film is subjected to heat treatment to generate hydrogen.
It is an oxide semiconductor film that has been purified by intentionally removing impurities such as water, hydroxyl groups, and hydrides (also referred to as hydrogen compounds) from the oxide semiconductor film.

Further, since the heat treatment is performed in a state where the oxide semiconductor film and the metal oxide film 631 containing oxygen are in contact with each other, it is one of the main component materials constituting the oxide semiconductor which is reduced at the same time by the removal process of impurities. Oxygen can be supplied to the oxide semiconductor film from the metal oxide film 631 containing oxygen. Therefore, the oxide semiconductor film is made more pure and electrically made i-type (intrinsic).

Therefore, the transistor 640 containing the highly purified oxide semiconductor film is electrically stable because the fluctuation of electrical characteristics is suppressed. Therefore, it is possible to provide a highly reliable semiconductor device as the semiconductor device of the present embodiment.

The electrode layer 641 is electrically connected to the conductive layer 643 formed on the interlayer insulating layer 634, and the electrode layer 642 is electrically connected to the gate electrode 645 via the electrode layer 644. Gate electrode 6
Reference numeral 45 is electrically connected to the gate electrode of the transistor 640, and the photodiode 6
02 is electrically connected to the transistor 640.

Here, a semiconductor layer having a p-type conductive type as the first semiconductor layer 606a, a high-resistance semiconductor layer (i-type semiconductor layer) as the second semiconductor layer 606b, and an n-type conductive type as the third semiconductor layer 606c are used. An example is a pin-type photodiode in which a semiconductor layer having a semiconductor layer is laminated.

The first semiconductor layer 606a is a p-type semiconductor layer, and can be formed of an amorphous silicon film containing an impurity element that imparts the p-type. The first semiconductor layer 606a is formed by a plasma CVD method using a semiconductor material gas containing an impurity element of Group 13 (for example, boron (B)). _{Silane (SiH 4} ) may be used as the semiconductor material gas. Or S
i ₂ H ₆ , SiH ₂ Cl ₂ , SiHCl ₃ , SiCl ₄ , SiF _{4, and the} like may be used. Further, after forming an amorphous silicon film containing no impurity element, the impurity element may be introduced into the amorphous silicon film by using a diffusion method or an ion implantation method. It is preferable to diffuse the impurity element by heating or the like after introducing the impurity element by an ion implantation method or the like. In this case, as a method for forming the amorphous silicon film, the LPCVD method, the vapor phase growth method, etc.
Alternatively, a sputtering method or the like may be used. The film thickness of the first semiconductor layer 606a is 10 nm or more 5
It is preferably formed so as to be 0 nm or less.

The second semiconductor layer 606b is an i-type semiconductor layer (intrinsic semiconductor layer) and is formed of an amorphous silicon film. To form the second semiconductor layer 606b, an amorphous silicon film is formed by a plasma CVD method using a semiconductor material gas. As the semiconductor material gas, silane (SiH ₄ ) may be used. Alternatively, Si ₂ H ₆ , SiH ₂ Cl ₂ , SiHCl ₃ , S
iCl ₄ , SiF _{4, and the} like may be used. The formation of the second semiconductor layer 606b is performed by the LPCVD method.
It may be carried out by a vapor phase growth method, a sputtering method or the like. The film thickness of the second semiconductor layer 606b is 2.
It is preferably formed so as to be 00 nm or more and 1000 nm or less.

The third semiconductor layer 606c is an n-type semiconductor layer, and is formed of an amorphous silicon film containing an impurity element that imparts the n-type. The third semiconductor layer 606c is formed by a plasma CVD method using a semiconductor material gas containing an impurity element of Group 15 (for example, phosphorus (P)). _{Silane (SiH 4} ) may be used as the semiconductor material gas. Or Si ₂ H ₆ ,
SiH ₂ Cl ₂ , SiHCl ₃ , SiC ₄ , SiF _{4, and the} like may be used. Further, after forming an amorphous silicon film containing no impurity element, the impurity element may be introduced into the amorphous silicon film by using a diffusion method or an ion implantation method. It is preferable to diffuse the impurity element by heating or the like after introducing the impurity element by an ion implantation method or the like. In this case, as a method for forming the amorphous silicon film, an LPCVD method, a vapor phase growth method, a sputtering method, or the like may be used. The film thickness of the third semiconductor layer 606c is preferably formed to be 20 nm or more and 200 nm or less.

Further, the first semiconductor layer 606a, the second semiconductor layer 606b, and the third semiconductor layer 606c may be formed by using a polycrystalline semiconductor instead of an amorphous semiconductor, or a microcrystal (Semi Amorphous Semiconductor: Semi-amorphous). SAS)) It may be formed by using a semiconductor.

Microcrystalline semiconductors belong to a metastable state between amorphous and single crystal, considering the free energy of Gibbs. That is, it is a semiconductor having a third state that is stable in free energy, has short-range order, and has lattice distortion. Columnar or acicular crystals grow in the normal direction with respect to the substrate surface. Microcrystalline silicon, which is a typical example of microcrystalline semiconductor, has its Raman spectrum shifted to a lower wavenumber side than ^{520 cm -1, which indicates single crystal silicon.}
That is, 520 cm ^{-1 indicating single crystal silicon and 480 cm −} indicating amorphous silicon.
There is a peak in the Raman spectrum of microcrystalline silicon between ^1. It also contains at least 1 atomic% or more of hydrogen or halogen to terminate the dangling bond.
Further, by adding rare gas elements such as helium, argon, krypton, and neon to further promote the lattice strain, the stability is increased and a good polycrystalline semiconductor film can be obtained.

This microcrystalline semiconductor film can be formed by a high-frequency plasma CVD method having a frequency of several tens of MHz to several hundreds of MHz, or a microwave plasma CVD apparatus having a frequency of 1 GHz or more. Typically, SiH ₄ , Si ₂ H ₆ , SiH ₂ Cl ₂ , SiHCl ₃ , SiCl ₄ , S.
The silicon-containing gas such as iF ₄ can be formed by dilution with hydrogen. Also, in addition to hydrogen
A microcrystalline semiconductor film can be formed by diluting a silicon-containing gas with one or more rare gas elements selected from helium, argon, krypton, and neon. At these times, the flow rate ratio of hydrogen to the silicon-containing gas is 5 times or more and 200 times or less, preferably 50 times or more and 150 times or less, and more preferably 100 times. Further, a hydrocarbon gas such as _{CH 4} , C ₂ H ₆ or a germanium-containing gas such as _{GeH 4} or GeF _{4 , F 2} or the like may be mixed in the silicon-containing gas.

Further, since the mobility of holes generated by the photoelectric effect is smaller than the mobility of electrons, the pin-type photodiode shows a characteristic that it is better to use the p-type semiconductor layer side as the light receiving surface. Here, p
Photodiode 602 from the surface of the substrate 601 on which the in-type photodiode is formed
An example of converting the light 622 received by the light into an electric signal is shown. Further, since the light from the semiconductor layer side having the conductive type opposite to the semiconductor layer side used as the light receiving surface becomes ambient light, the electrode on the semiconductor layer side having the conductive type opposite to the semiconductor layer side used as the light receiving surface. As the layer, it is preferable to use a conductive film having a light-shielding property. Also,
The n-type semiconductor layer side can also be used as the light receiving surface.

As the metal oxide film 631, a gallium oxide film formed by a sputtering method may be used. Further, a film obtained by adding indium or zinc to gallium oxide may be used, and for example, a gallium oxide film containing 0.01 to 5 atomic% of indium or zinc can be used. By adding indium or zinc, the electrical conductivity of the metal oxide film 631 can be improved and the charge accumulation can be further reduced.

As the interlayer insulating layers 633 and 634, an insulating layer that functions as a flattening insulating film is preferable in order to reduce surface irregularities. As the interlayer insulating layers 633 and 634, for example, an organic insulating material such as polyimide, acrylic resin, benzocyclobutene resin, polyamide or epoxy resin can be used. Further, in addition to the above organic insulating material, a single layer such as a low dielectric constant material (low-k material), a siloxane resin, PSG (phosphorus glass), BPSG (phosphorus glass), or a laminate can be used.

As the interlayer insulating layer 633 and the interlayer insulating layer 634, an insulating material is used, and depending on the material, a sputtering method, a spin coating method, a dipping method, a spray coating, and a droplet ejection method (inkjet method, screen printing, offset). It can be formed by using (printing, etc.), roll coating, curtain coating, knife coating, or the like.

By detecting the light 622 incident on the photodiode 602, the information of the object to be detected can be read. A light source such as a backlight can be used when reading the information of the object to be detected.

As the transistor 640, the transistor shown as an example in the first or second embodiment can be used. Transistors containing an oxide semiconductor film that has been purified by intentionally removing impurities such as hydrogen, water, hydroxyl groups, and hydrides (also called hydrides) from the oxide semiconductor film have fluctuations in the electrical characteristics of the transistor. It is suppressed and electrically stable. Further, the transistor having a metal oxide film having an antistatic function can prevent the generation of parasitic channels on the back channel side of the oxide semiconductor film. Further, by preventing the generation of parasitic channels on the back channel side of the oxide semiconductor film in the transistor, fluctuations in the threshold voltage can be suppressed. Therefore, it is possible to provide a highly reliable semiconductor device.

This embodiment can be implemented in combination with the configurations described in other embodiments as appropriate.

(Embodiment 5)
The liquid crystal display device disclosed in the present specification can be applied to various electronic devices (including game machines). Examples of electronic devices include television devices (also referred to as televisions or television receivers), monitors for computers, digital cameras, cameras such as digital video cameras, digital photo frames, and mobile phones (mobile phones, mobile phones). (Also referred to as a device), a portable game machine, a mobile information terminal, a sound reproduction device, a large game machine such as a pachinko machine, and the like. An example of an electronic device including the liquid crystal display device described in the above embodiment will be described.

FIG. 7A is an electronic book (also referred to as an E-book), which is a housing 9630 and a display unit 9631.
, Operation key 9632, solar cell 9633, charge / discharge control circuit 9634. The electronic book shown in FIG. 7A has a function of displaying various information (still images, moving images, text images, etc.), a function of displaying a calendar, a date or time, etc. on the display unit, and information displayed on the display unit. It can have a function of operating or editing a computer, a function of controlling processing by various software (programs), and the like. Note that FIG. 7A shows a configuration having a battery 9635 and a DCDC converter (hereinafter abbreviated as a converter) 9636 as an example of the charge / discharge control circuit 9634. By applying the semiconductor device shown in any one of the first to fourth embodiments to the display unit 9631, a highly reliable electronic book can be obtained.

With the configuration shown in FIG. 7A, when a transflective or reflective liquid crystal display device is used as the display unit 9631, it is expected to be used in relatively bright conditions, and the solar cell 9633.
It is preferable because it can efficiently generate electricity and charge the battery 9635.
Since the solar cell 9633 can be appropriately provided in an empty space (front surface or back surface) of the housing 9630, it is suitable because it can be configured to efficiently charge the battery 9635. As the battery 9635, if a lithium ion battery is used, there is an advantage that the size can be reduced.

Further, the configuration and operation of the charge / discharge control circuit 9634 shown in FIG. 7 (A) will be described by showing a block diagram in FIG. 7 (B). FIG. 7B shows the solar cell 9633, the battery 9635, the converter 9636, the converter 9637, the switches SW1 to SW3, and the display unit 9631, and the battery 9635, the converter 9636, the converter 9637, and the switches SW1 to SW3 are charged and discharged. This is the part corresponding to the control circuit 9634.

First, an example of operation when power is generated by the solar cell 9633 by external light will be described.
The electric power generated by the solar cell 9633 is stepped up or down by the converter 9636 so as to be a voltage for charging the battery 9635. Then, when the power from the solar cell 9633 is used for the operation of the display unit 9631, the switch SW1 is turned on and the converter 9 is turned on.
At 637, the voltage required for the display unit 9631 is stepped up or down. Further, when the display is not performed on the display unit 9631, the SW1 may be turned off and the SW2 may be turned on to charge the battery 9635.

Next, an example of operation when power is not generated by the solar cell 9633 due to external light will be described. The electric power stored in the battery 9635 is stepped up or down by the converter 9637 by turning on the switch SW3. Then, the electric power from the battery 9635 is used for the operation of the display unit 9631.

Although the solar cell 9633 is shown as an example of the charging means, the battery 9635 may be charged by another means. Further, the configuration may be performed by combining other charging means.

FIG. 8A shows a notebook-type personal computer, which has a main body 3001 and a housing 3002.
, Display unit 3003, keyboard 3004, and the like. By applying the semiconductor device shown in any one of the first to fourth embodiments to the display unit 3003, a highly reliable notebook personal computer can be obtained.

FIG. 8B is a personal digital assistant (PDA), and the main body 3021 is provided with a display unit 3023, an external interface 3025, an operation button 3024, and the like. There is also a stylus 3022 as an accessory for operation. By applying the semiconductor device shown in any one of the first to fourth embodiments to the display unit 3023, a more reliable personal digital assistant (PDA) can be used.
Can be.

FIG. 8C shows an example of an electronic book. For example, an electronic book is composed of two housings, a housing 2701 and a housing 2703. The housing 2701 and the housing 2703 are integrated by a shaft portion 2711, and the opening / closing operation can be performed with the shaft portion 2711 as an axis. With such a configuration, it is possible to perform an operation like a paper book.

A display unit 2705 is incorporated in the housing 2701, and a display unit 2707 is incorporated in the housing 2703. The display unit 2705 and the display unit 2707 may be configured to display a continuous screen or may be configured to display different screens. By displaying different screens, for example, a sentence is displayed on the right display unit (display unit 2705 in FIG. 8 (C)), and an image is displayed on the left display unit (display unit 2707 in FIG. 8 (C)). Can be displayed. By applying the semiconductor device shown in any one of the first to fourth embodiments to the display unit 2705 and the display unit 2707, a highly reliable electronic book can be obtained.

Further, FIG. 8C shows an example in which the housing 2701 is provided with an operation unit or the like. For example, the housing 2701 includes a power supply 2721, operation keys 2723, a speaker 2725, and the like. The page can be fed by the operation key 2723. A keyboard, a pointing device, or the like may be provided on the same surface as the display unit of the housing. Further, the back surface or the side surface of the housing may be provided with an external connection terminal (earphone terminal, USB terminal, etc.), a recording medium insertion portion, or the like. Further, the electronic book may be configured to have a function as an electronic dictionary.

Further, the electronic book may be configured so that information can be transmitted and received wirelessly. It is also possible to purchase and download desired book data or the like from an electronic book server wirelessly.

FIG. 8D shows a mobile phone, which is composed of two housings, a housing 2800 and a housing 2801. The housing 2801 includes a display panel 2802, a speaker 2803, a microphone 2804, a pointing device 2806, a camera lens 2807, and an external connection terminal 2.
It is equipped with 808 and the like. Further, the housing 2800 is provided with a solar cell 2810 for charging a mobile phone, an external memory slot 2811, and the like. In addition, the antenna is a housing 280.
1 Built in inside. By applying the semiconductor device shown in any one of the first to fourth embodiments to the display panel 2802, a highly reliable mobile phone can be obtained.

Further, the display panel 2802 includes a touch panel, and in FIG. 8D, a plurality of operation keys 2805 displayed as images are shown by dotted lines. A booster circuit for boosting the voltage output by the solar cell 2810 to a voltage required for each circuit is also mounted.

The display direction of the display panel 2802 changes as appropriate according to the usage pattern. Further, since the camera lens 2807 is provided on the same surface as the display panel 2802, a videophone can be made. Speaker 2803 and microphone 2804 are not limited to voice calls, but videophones,
Recording and playback are possible. Further, the housing 2800 and the housing 2801 can be slid and changed from the unfolded state as shown in FIG. 8D to the overlapping state, and can be miniaturized suitable for carrying.

The external connection terminal 2808 can be connected to various cables such as an AC adapter and a USB cable, and can be charged and data communication with a personal computer or the like is possible. Further, a recording medium can be inserted into the external memory slot 2811 to support storage and movement of a larger amount of data.

Further, in addition to the above functions, an infrared communication function, a television reception function, and the like may be provided.

FIG. 8E is a digital video camera, which is composed of a main body 3051, a display unit (A) 3057, an eyepiece unit 3053, an operation switch 3054, a display unit (B) 3055, a battery 3056, and the like. The semiconductor device shown in any one of the first to fourth embodiments is displayed on the display unit (
By applying it to A) 3057 and display unit (B) 3055, a highly reliable digital video camera can be obtained.

FIG. 8F shows an example of a television device. In the television device 9600, the display unit 9603 is incorporated in the housing 9601. The display unit 9603 makes it possible to display an image. Further, here, a configuration in which the housing 9601 is supported by the stand 9605 is shown. The semiconductor device shown in any one of the first to fourth embodiments is displayed on the display unit 9603.
By applying to, it is possible to obtain a highly reliable television device.

The operation of the television device 9600 can be performed by an operation switch included in the housing 9601 or a separate remote control operating device. Further, the remote controller operating device may be provided with a display unit for displaying information output from the remote controller operating device.

The television device 9600 is configured to include a receiver, a modem, and the like. The receiver can receive general television broadcasts, and by connecting to a wired or wireless communication network via a modem, it can be unidirectional (sender to receiver) or bidirectional (sender and receiver). It is also possible to perform information communication between (or between recipients, etc.).

This embodiment can be implemented in combination with the configurations described in other embodiments as appropriate.

400 Substrate 401 Gate electrode 402 Gate insulating film 403 Oxide semiconductor film 405a Source electrode 405b Drain electrode 407 Metal oxide film 410 Transistor 431 Metal oxide film 441 Oxide semiconductor film 601 Substrate 602 Photodiode 606a Semiconductor layer 606b Semiconductor layer 606c Semiconductor layer 608 Adhesive layer 613 Substrate 631 Metal oxide film 633 Interlayer insulation layer 634 Interlayer insulation layer 640 Transistor 641 Electrode layer 642 Electrode layer 643 Conductive layer 644 Electrode layer 645 Gate electrode 656 Transistor 658 Photodiode reset signal line 659 Gate signal line 671 Photosensor output signal Line 672 Photosensor Reference signal line 2701 Housing 2703 Housing 2705 Display 2707 Display 2711 Shaft 2721 Power supply 2723 Operation key 2725 Speaker 2800 Housing 2801 Housing 2802 Display panel 2803 Speaker 2804 Microphone 2805 Operation key 2807 Pointing device 2807 Camera Lens 2808 External connection terminal 2810 Solar cell 2811 External memory slot 3001 Main unit 3002 Housing 3003 Display unit 3004 Keyboard 3021 Main unit 3022 Stylus 3023 Display unit 3024 Operation button 3025 External interface 3051 Main unit 3053 Eyepiece 3054 Operation switch 3055 Display unit ( B)
3056 Battery 3057 Display (A)
4001 Substrate 4002 Pixel part 4003 Signal line drive circuit 4004 Scanning line drive circuit 4005 Sealing material 4006 Substrate 4008 Liquid crystal layer 4010 Transistor 4011 Transistor 4013 Liquid crystal element 4015 Connection terminal electrode 4016 Terminal electrode 4018 FPC
4018a FPC
4018b FPC
4019 Anisotropic conductive film 4020 Metal oxide film 4021 Insulation layer 4023 Insulation film 4030 Electrode layer 4031 Electrode layer 4032 Insulation film 4033 Insulation film 4510 Partition 4511 Electric discharge layer 4513 Light emitting element 4514 Filling material 4612 Cavity 4613 Spherical particle 4614 Filling material 4615a Black Area 4615b White area 9600 Television device 9601 Housing 9603 Display 9605 Stand 9630 Housing 9631 Display 9632 Operation key 9633 Solar cell 9634 Charge / discharge control circuit 9635 Battery 9636 Converter 9637 Converter

Claims (1)

It has a plurality of pixels having a transistor, a liquid crystal element electrically connected to the transistor, and a holding capacity.
The transistor has an oxide semiconductor film that functions as a channel forming region, and a gate electrode that overlaps the oxide semiconductor film on the first surface side of the oxide semiconductor film.
A metal oxide film in contact with the second surface of the oxide semiconductor film is provided on the second surface side of the oxide semiconductor film facing the first surface.
The oxide semiconductor film has In, Ga, and Zn, and has In, Ga, and Zn.
The metal oxide film may have a gallium oxide added with indium 0.01-5 atomic%,
The hydrogen content of the metal oxide film is lower than the hydrogen content of the oxide semiconductor film.
A liquid crystal display device having a holding capacity of 1/3 or less of the capacity value of the liquid crystal element.

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